The present invention relates to an ink-jet type printing machine, more particularly, a printing machine for printing a clear printing image on surfaces of cardboard sheets.
Japanese Patent document No. H03-121853A discloses an ink-jet type printing machine for cardboard sheets. This printing machine has a transfer device having a conveyor having suction holes for transferring the cardboard sheets one by one, a suction device for sucking one of two surfaces of each of the cardboard sheets, which faces the conveyor, through the suction holes, and ink jet heads spaced apart from the other of the two surfaces to be printed, the ink jet heads being located at the side of the other of the two surfaces to be spaced apart therefrom. The ink jet heads have ink jet nozzles and are located so as to maintain a desired distance between tips of the ink jet heads and the printing surface.
In accordance with above described constructions, the cardboard sheets are suctioned toward the conveyor via suction holes of the suction device and cardboard sheets are conveyed by the conveyor. When the cardboard sheets move across the ink jet heads, the ink droplets are jetted out toward the printing surface and land on the printing surface, whereby a printing image can be created.
However, the prior art printing machine has the following technical drawbacks.
It is important that the cardboard sheets are suctioned toward the conveyor by the suction device in order to prevent warp of the cardboard sheet or shifting of the cardboard sheets relative to the conveyor. At this time, a gap can be formed between adjacent sheets in the feeding direction because the sheets are transferred one by one. Since the holes on the gap portion is not covered with the cardboard sheet, suction air from the suction device is released through the gaps toward a space in which ink jet heads are disposed.
As a result, the environment between the ink jet heads and the printing surface will be disturbed, so that ink droplets are deflected before reaching the printing surface, and thus the deviation of the position of dots from the desired position can be caused, which causes unclear printing or even causes unsatisfactory printing result. However, because ink jet heads include a number of ink jet nozzles, it is almost impossible to adjust each of them in order to prevent such a deviation.
The object of the present invention is to provide an ink jet type printing machine which can print clear images on the desired position of an individual cardboard sheet.